Question

$1.78\, g$ of an optically active L-amino acid $(A)$ is treated with $NaNO_2/HCl$ at $0\,{}^\circ\,C$. $448\, cm^3$ of nitrogen was at $STP$ is evolved. A sample of protein has $0.25\%$ of this amino acid by mass. The molar mass of the protein is

• A. $34,500 \,g \,mol^{-1}$
• B. $34,600 \,g \,mol^{-1}$
• C. $36,500 \,g \,mol ^{-1}$
• D. $35,600\, g\, mol ^{-1}$

Answer 1

Answer: (D)

From van-Siyke method for estimation of amino acids



Molar mass of L-amino acid $=\frac{1.78 \times 22400}{448}$

$=89$

$\because$ Protein has $0.25 \%$ of amino acid by mass

$\therefore $ Molar mass of protein $=\frac{89 \times 100}{0.25}$

$=35600\, g\, mol ^{-1}$